She's had the worst week of her life. Now, as she goes on the run with a photographer who once stalked her, an insider who knows her well reveals she's been fighting manic depression for a year...

The young woman was adamant: "They're not sending me to the nut house," she shouted into her mobile phone.

"No one can make me go if I don't want to go, and I ain't goin'."

It was last Tuesday evening and Britney Spears was talking to a close friend as she cruised down Sunset Boulevard in her black sports car, followed by the swarm of paparazzi that pursues her everywhere she goes.

As the friend tried to reason with the star, her words - and her driving - became increasingly erratic.

"See that? I just went through another stop sign," Britney shrieked. "See what you made me do? I'm gonna hurt someone out here!" Then the 26-year-old made a chilling promise: "I'll kill myself before I let them lock me up again. So tell Mama and Daddy I said so!"

Just before she hung up, she uttered a final few words.

And as someone who has known and liked Britney for almost a decade, I find what she had to say utterly chilling.

"Oh my God," she moaned. "It's over for me."

In one short week, it seems, Britney's life has become a living nightmare, turning a troubled young star into a woman on the brink of insanity.

The crisis began last weekend, when a four-hour police stand-off at her Los Angeles home over custody of her two young children ended with Britney being strapped to an ambulance trolley and dragged off to the mental ward of a hospital.

As a result, she's been stripped of all custody of her children.

Meanwhile, her frantic parents are racking their brains, trying to figure out how to have their tormented young daughter formally committed to an institution.

And to add to the mess, a British paparazzo whom Britney has just taken into her confidence - and her bed - has already betrayed that trust in the most sordid way. For several years, Adnan Ghalib has been one of the many photographers who earns a wage simply by following Britney Spears's every move.

Originally from Afghanistan, he moved with his family to London in 1977 as a five-year-old refugee, later settling in California, where he managed a strip bar before branching out as a paparazzo.

Though married, he's been separated from his wife, Azlynn Berry, for about a year.

So how did this 35-year-old low-life end up sleeping with the star he was stalking?

"Britney has been slipping off to hotels and spending the night with this guy for a couple of weeks now," says one disgusted friend of the singer.

"It started on December 23 when they spent the night together at the Peninsula in Beverly Hills. He's a creepy guy.

"He always said he would one day get Britney Spears in the sack, and I guess he finally has. She's giddy when she's around him. But I think he's out to use her."

Quite so. For on Wednesday, Britney learned that Ghalib had been attempting to sell pictures of Britney wearing only her knickers.

The asking price? A million dollars, cash.

He has now reportedly settled for a little more than £25,000 from an Australian magazine. Given such a betrayal, one would think Britney would be outraged. But far from it. At the time of writing, Ghalib was still by her side.

On Wednesday, the pair boarded a private jet, heading for Mexico, arriving back in LA on Thursday night when Britney was pictured sitting in a car at a petrol station, wearing glasses and her favoured disguise of a bizarre neon pink bobbed wig - all the while puffing on an unidenitified inhaler, in clear view of watching photographers.

Such odd behaviour has left her friends as mystified as they are concerned. But it says a great deal about Britney's emotional state.

"She's used to people exploiting her," says one of her close confidantes. "She once told me: 'If I cut everyone out of my life who has tried to make a buck off me, I'd have no one.'

"She feels she's been exploited by lovers, assistants, managers, her ex-husband, her parents. Why should Ghalib be any different?

"So, as far as I know, she's still sleeping with the enemy, at least for now. But she can't make rational decisions, anyway. She's too messed up. This girl needs help, badly." A fearful relative agrees: "Actually, it's been this way for months.

"People assume that she's been on illegal drugs and, of course, she has been in the past.

"But most of that stopped months ago when the court ordered frequent drug tests in the child custody case between her and Kevin (Federline, her ex-husband).

"The only drugs she's on right now are certain prescription medications she's taking for extreme anxiety and ADD (Attention Deficit Disorder), and that includes Adderall, which is a powerful amphetamine.

"Actually, I think the Adderall is ruining her," continued the family member.

"It makes her manic. But that's the least of her problems.

"What no one in the family wants to admit is that she's probably bi-polar" - a form of manic depression that leads to wild mood swings. Indeed, I can confirm that Britney was diagnosed as being "suspected bipolar" when she was in Promises rehab in Santa Monica, California, last year.

Doctors there also thought she was suffering from a borderline personality disorder.

However, a final diagnosis couldn't be made without additional tests, which Britney refused to undertake.

The Spears family has been desperately trying to get a conclusive diagnosis. But the problem is, without Britney's cooperation, there's no way to do it.

"And now that she's let it go on too long, she's totally bonkers," said her relative.

"I have actually been with her when she's bashed her head against a wall, trying to hurt herself.

"She needs to be in a hospital, but she won't go. She'll have to be committed. That's the only way."

Now, in desperation, the singer's parents - Jamie and Lynne Spears - along with Kevin Federline, have begun to undertake drastic action to help Britney.

They are considering "a number of different scenarios".

But the most extreme option is for them to go to court and get an order that would force Britney into in-patient treatment.

If that happens, Britney would be forcibly detained by police on a '5150' - a formal charge meaning that she's a danger to herself or others. Then, while she's in a hospital, doctors would appeal to the County Public Guardian, who would go to court and ask for power of attorney.

Britney could then be involuntarily committed to a mental hospital for her own good. Whether or not all of this can be co-ordinated remains to be seen.

But if what took place when police raided Britney's home on January 3 is any indication, she's in desperate need of professional help. A police source gave me a chilling account of the four-hour stand-off, which began when Britney refused to hand over her children, Sean Preston, two, and Jayden James, 16 months, to Kevin Federline's bodyguards, at the end of her supervised access day.

The court-appointed monitor was able to get Sean Preston outside and into the bodyguard's vehicle.

But by the time she went back in for Jayden James, Britney had locked herself in the bathroom with the toddler.

By 10.45pm police had been summoned, and the stand-off was still going on with the child screaming and crying the whole time.

With Britney still refusing to surrender him, it had soon turned into a hostage situation. Fire engines and ambulances arrived with police helicopters hovering overhead and an army of paparazzi on the ground.

There was a very real fear that Britney would kill Jayden, and then herself. In fact, one source told me that there was a stage when Kevin Federline truly believed that his son was already dead.

But at 11.40pm, the authorities somehow convinced Britney to let them into the bathroom. Once they were with her, they actually had to wrestle Jayden away from her. The boy was so traumatised, he was immediately taken to Cedars-Sinai Hospital in an ambulance. Paramedics then strapped Britney - who was alternately sobbing and laughing - to a trolley and loaded her into another ambulance.

She was also taken to Cedars, where she was admitted to a mental ward on a 72-hour watch.

In the subsequent Press furore, it was widely reported that Spears had a gun in the house, but I have learned that this is untrue.

"There is no way that anyone who knows Britney would allow her to have a gun during a supervised visit with her children," says a source close to the Spears family.

Nor is it true that her behaviour was the result of a cocktail known as a 'purple monster' - a mix of vodka, NyQuil painkillers and Red Bull, which the star was said to have downed, along with 100 different prescription pills (including Vicodin, Ritalin and sleeping pills).

Paul L. Doering, professor of pharmacy at the University of Florida, says that no person of Britney's height and weight could have survived such a lethal mix. Hospital officials have also confirmed that there were no illegal drugs in Britney's system.

Of course, that does not rule out the possibility that she had taken some combination of mood-altering pharmaceuticals.

Her behaviour in hospital was certainly bizarre, to say the least.

"At times she was very quiet, then other times absolutely frantic," says one of the nurses who attended her.

"Everyone was afraid for her and even of her."

"At one point, she was crying about her sister (16-year-old Jamie Lynn) being pregnant, saying she would now be ruined, too.

"She was railing against her parents for screwing up both her life and her sister's. I mean, she was a real mess.

"Then, 15 minutes later, she would be sound asleep. She'd then wake up feeling very calm and happy. It was all very sad."

Oddly, the nurse also told me that Britney insisted on speaking to the hospital staff using a clipped, British accent (a common symptom, says one psychologist I have spoken to, of a personality disorder).

As the doctors struggled for a formal diagnosis, Britney's parents rushed to her bedside, pleading with her to agree to psychiatric treatment.

But the star would not listen, screaming at her father: "You're not going to lock me up! You can forget it. I'm not going."

A further attempt by psychologist Dr Phil McGraw - who has a popular talk show here in the States - to persuade Britney to seek treatment also backfired horribly.

He barged into her room, at the invitation of her parents, subsequently giving a statement to the media saying: "My meeting with Britney leaves me convinced more than ever that she is in dire need of both medical and psychological intervention."

But it was to no avail. Refusing to recognise that she was ill, the star discharged herself from the hospital, leaving Kevin Federline in such fear of his family's safety that a restraining order has been now placed against her.

She is not allowed anywhere near him, or the children.

This latest twist has left Britney's friends in even greater fear for her sanity.

"The kids are her life," says one of her confidantes.

"She told me that she has no reason to live if she can't see her kids. So, yes, I'm afraid. Very afraid."

And with good reason, it would seem.

"A woman like Ms Spears who has exhibited this kind of frightening behaviour is a likely candidate for suicide," explains one Beverly Hills psychiatrist, who asked to remain anonymous.

"She has isolated herself exactly the way people suffering from this disorder do, cutting everyone out who can help.

"I truly believe she will not live through the year if she's not placed in involuntary mental health treatment.

"All of these incidents, from the photos last year of her baring her crotch to the shearing off of her hair... well, it sounds to me as if she's been living in a world of unreality for a long time."

His comments reminded me of an incident I witnessed three years ago, when Britney was at the height of her fame.

She and I were chatting at a hotel in Los Angeles, when she became panicked by the paparazzi who had gathered outside the building.

"Don't worry, we'll call in the double," said one of her handlers.

And sure enough, within 20 minutes a young woman who was the spitting image of Britney showed up at the hotel.

"Oh, thank God you made it," the star told her. Then the two went into a closet and switched clothing.

As the doppelganger made her exit, we watched from above while photographers went berserk taking the double's picture, setting off in hot pursuit when she left in Britney's car.

"Those dummies. They are so stupid. Look at them!" said Britney, relishing the deception.

"I don't know what I'd do if I actually had to live my own life 24 hours a day. Why, I think I'd go crazy."

And now? Britney's sleeping with one of those "dummies", her life is in tatters and her mind is increasingly unhinged.